Bladed rotors



A. E. H. ELMER 3,260,312

BLADED ROTORS July 12, 1966 Filed Sept. 28. 1964 IMVENTOE Amy/t E. H. ELMEZ ATTORNEY United States Patent 3,260,312 BLADED ROTORS Arthur E. H. Elmer, Painswick, England, assignor to Dowty Hydraulic Units Limited, Cheltenham, England, a British company Filed Sept. 28, 1964, Ser. No. 399,623 Claims priority, application Great Britain, Oct. 1, 1963, 38,704/63 4 Claims. (Cl. 170-1605) This invention relates to bladed rotors, such as may constitute a fan for cooling an internal combustion engine. According to this invention the blades of the fan adjust automatically in pitch (or the equivalent thereof) in accordance with the fans rotational speed, so that at higher speeds it will assume a fine pitch position, and at lower speeds it will assume coarse pitch position. This ability for self-adjustment in fan blades is known-see for example my copending Patent No. 3,220,484, dated November 30, 1965but always heretofore each blade was subject to a centrifugal twisting moment which the inherent in the blade as constructed, and which was not itself governed by parameters purposely incorporated in the blades design, and/or capable of revision from time to time to suit different operating conditions, so that a single fan design, incorporating differing weight elements but otherwise unchanged, can accommodate a rather wide range of operating conditions.

In addition to the above object, it is an object to provide such a bladed rotor that can be made simply and inexpensively, and in at least one form that can be varied in its characteristics in a simple manner, as the operating conditions may require.

A further object is to provide a novel hub, weight, and sheath construction fully integrated into a fan, and which in at least the one form enables change in the fans characteristics by replacement of its weights by weights of different mass, or differently arranged.

In one form the hub may comprise two metallic members coaxially arranged and held together in the axial sense by rivets or equivalent means which themselves may serve as anchorages for structure incorporated within the blades, specifically, certain torsionally resilient backbone and weight-supporting members.

The blade sheaths and the hub covering may be integrated with or separable from the backbone members and their supported weights. In the form wherein the blades and the hub covering are integral-whether or not the backbones and weights are also integral therewith-both may be of resilient plastics material and formed by a moulding process, whereby the annular hub members and weighted backbones are encased therein.

One embodiment of the invention will now be particularly described by way of example with reference to the accompanying drawing.

Referring to the drawing, a bladed rotor in the form of a cooling fan 10, shown as having four blades 11, and which is suitable for use in a road vehicle for cooling the engine of the vehicle, comprises a hub 12 which may be bolted in known manner to a pulley (not shown) mounted so that it may be driven in the usual manner,

through belt or other means, by the engine, suitablebolt holes 13 being provided in the hub for this purpose.

The hub comprises two steel members 14 and 15 of annular shape co-axially arranged and secured together in the axial sense by rivets, one of which is shown at 16 in the cut-away portion of the drawing. The member 15 is partly milled away at 17 on that face thereof adjacent the member 14 and in the zone of the rivet 16 to provide an opening in the assembly whereby a backbone member 18 for each blade can 'be anchored to the respective rivets 16.

Each backbone member 18 is of a resilient material such as spring steel and affords resilience in torsion. The backbone member forms a part of a skeleton-like frame, one such frame 19 for each blade. At several positions along the length of the backbone member transversely-arranged weight bars 20 are provided, these being secured rigidly to the member 18.

The metallic hub structure formed by the members 14 and 15 and also the blade frames 19 are encased in an integral hub cover and blade sheathing structure 21 of resilient material, such as a resilient plastics material. In this way the flexible sheathing defines the working surfaces of the blades, the frames 19 providing a metallic reinforcement anchored with respect to the hub.

By virtue of the construction of the blades, each is capable of automatic adjustment as to the amount of twist along its length, under the influence of centrifugal twisting moment, such twist corresponding to a change in the pitch of the blades in the decreasing, fining direction, with increase in rotational speed of the fan. The weight bars 20 are so arranged with respect to the backbone member 18 and the resilient sheathing, that with torsion of the member each weight bar has a slightly different angular position with respect to the adjacent one, in dependence upon the degree of twist applied.

The fan is constructed by firstly assembling the metallic annular members 14 and 15 together by the rivets 16, the frames 19 of each blade being anchored to the respective rivets 16. Assuming that the sheathing is moulded of plastics material, the metallic structure is then placed in the base of a mould of suitable shape, an extension portion of each backbone member locating its blade frame accurately within the base of the mould. The mould cover is then placed over the base of the mould, the configuration then defined by the assembled mould and enclosing the metallic hub and blade frame structure representing the final integral shape of the bladed rotor.

Plastics material in a heated and thus fluid state is then introduced by a known injection technique into the interior of the mould thereby to encase the metallic hub and blade frame structure.

When the resilient plastics material has set, the mould is opened and the completed bladed rotor structure is removed, whereupon the extension portions of the backbone members 18 are cut from the tips of the blades.

In operation of the above-described cooling fan it is required that during relatively slow speed running, the fan should be in a relatively coarse pitch condition, but is required progressively to decrease in pitch with increase in speed of rotation so that the cooling air passed by the fan over the engine is maintained substantially constant. Thus, at the higher rotational speeds of the engine only sufficient power is absorbed from the engine to drive the fan at a pitch condition which provides just the right amount of air for cooling, and no excess air, with accompanying power absorption wastage, is required to be evident.

However, although in the previous paragraph reference has been made to blade pitch, variation in blade twist is the equivalent thereof, for it has a similar operational effect, and automatic control of blade twist is achieved under the effect of the centrifugal twisting moments inherent in the blade structures. The assembly of resilient sheath, torsion backbone member 18 and weight bars 20 is such that when the fan is rotating at relatively slow speeds the blades are maintained in a twist condition corresponding to a coarse pitch. As the speed of the fan increases, the centrifugal twisting moments inherent in the blade structures by virtue of the magnitude and spacing of the weight bars 20, commence to overcome the resilience in the spring steel backbone member 18 and in the material of the sheath of each blade.

As this occurs, the backbone member 18 is twisted and through the intermediary of the weight members, the resilient sheath is twisted also, so that the twist of the blade is varied in a sense corresponding to fining off in the pitch of the blades. Thus when the blades are in their coarse pitch position there is a degree of natural stiffness in the members 18 and the sheathing to hold them there, but when the centrifugal twisting moments increase upon increase in rotational speed of the fan, the natural stiffness in the members 18 and sheathing is overcome and twisting of the members and sheathing occurs in a direction in opposition to the torsional stiffness. Hence, torsion applied by virtue of centrifugal twisting moment overcomes the torsional resistance in the blades to move the blades towards fine pitch. As the centrifugal twisting moment reduces, upon reduction in rotational speed of the fan, the torsion stored in the member 18 is capable of overcoming the diminishing applied torsion and thus of moving the blades back in the pitch coarsening direction.

By so controlling the volume of air passing through the fan, the horse-power absorbed by the fan throughout its operational speed range increases by only a small amount from the low rotational speed condition to the high rotational speed condition as compared with the relatively larger power absorption by the fan occurring with fans of fixed pitch over a similar operational speed range.

With fixed pitch fans the relatively high power absorbed towards and at the higher speeds of operation of the fan are in excess of what is only actually necessary to satisfy the cooling demands of the engine. Therefore, the present invention ensures that such increase in power absorbed is reduced to such a marked extent as to have some advantageous effect in the economy of operation of the associated engine.

Further, reduction in noise level is advantageously achieved because of the lower power absorption at the higher engine operating speeds.

The fan in accordance with the invention may be arranged so that other means, for example, thermo-responsive devices, can additionally be incorporated in the fan and operable upon the blades to supplement the -centrifugal twisting moments in the blade twist varying function.

Although in the embodiment described with reference to the drawing, the blade sheaths are formed integrally with the resilient plastics covering of the hub structure, in an alternative embodiment of the invention the blade sheaths are formed separately from the hub structure, which need have no resilient plastics covering. In this case the root portions of the plastic blade sheaths are secured rigidly to the hub structure by suitable clamping means, but each blade sheath is not moulded around the weight bars, but is instead a tight sliding fit over the skeleton frame structure.

Here, variation in the centrifugal twisting moment characteristics can then be simply achieved by removal of the Weight bars and replacement by weight bars of different mass, or alternatively variation can be achieved by re-arranging the positions of the weight bars upon the backbone member.

Again, a range of different blade frames, having weight bars of predetermined mass and spacing, may be available for co-operation with a blade sheath of a given size, so that it is a simple matter to remove one and replace it by another in each of the blades of the fan for changing the operating characteristics to suit a particular engine installation.

Although in the embodiment described with reference to the drawing the back-bone member has an extension 'portion for locating the frame member in the mould during the moulding process, in another embodiment, and additionally, the end portions of each of the weight members are connected by their wires, one wire adjacent the leading edge and one adjacent the trailing edge. Both wires are also extended beyond the blade tip thereby to provide additional support of the frame structure in the mould.

The invention is in no way limited to production of the bladed rotor by an injection moulding technique as instead any suitable form of laying-up technique can be used, for example the laying-up over the frame of resinimpregnated glass fibre, thereafter cured in necessary manner.

Further, the invention is not limited to its application to a cooling fan of an engine, as equally well it may be applied to bladed rotors such as ram air turbines, automatic propellers for aircraft and the like, where the inherent centrifugal twisting moments in the blade structures can be utilised for controllability.

I claim as my invention:

1. A bladed rotor comprising:

(a) a rotat'ive hub,

(b) a plurality of generally-radially disposed blade frames, each of which includes a single longitudinal backbone member that is resiliently yieldable in torsion, anchored to the hub, and including also a number of weight bars which are fastened to the backbone member, disposed transversely of the blade and spaced at intervals along the back-bone member, each weight bar being of predetermined mass,

(c) flexible blade sheaths, one for each blade, enclosing the corresponding blade frames to form the working surfaces of the blades, and anchored in the radial sense with respect to the hub, and,

(d) each longitudinal backbone member and sheath being arranged to twist torsionally throughout the blades length under moments applied to the backbone member by the weights of predetermined mass, such twisting being thereby variable in accordance with the magnitude of centrifugal twisting moments inherent in the blade structure and acting on the mass of the blade frames at different rotational speeds.

2. A bladed rotor as claimed in claim 1, wherein the hub comprises two metallic members co-axially arranged and held together in the axial sense by rivet means themselves serving as anchorages for the backbone members of the respectiv blades.

3. A bladed rotor as claimed in claim 1, wherein the sheaths are of a moulded material, wherein the frames are incorporated integrally, and each sheath is formed with a flexible hub covering in which the hub is encased.

4. A bladed rotor as claimed in claim 3, wherein the covering of th blades and hub is a resilient plastics material wherein the hub and the blade frames are encased.

References ited by the Examiner UNITED STATES PATENTS 1,308,527 7/1919 Nilson "170-159 1,463,153 7/1923 Clay 170-159 1,757,292 5/1930 Caldwell 170-16051 2,359,265 9/1944 Ha'ckethal er al. 17016().16 3,033,293 5/1962 Bihlmire 170 159 3,044,557 7/1962 Posh l160.5

FOREIGN PATENTS 124,253 3/1919 Great Britain. 193,827 3/1924 Great Britain.

SAMUEL LEVINE, Primary Examiner.

JULIUS E. WEST, Examiner.

E. A. POWELL, JR., Assistant Examiner. 

1. A BLADED ROTOR COMPRISING: (A) A ROTATIVE HUB, (B) A PLURALITY OF GENERALLY-RADIALLY DISPOSED BLADE FRAMES, EACH OF WHICH INCLUDES A SINGLE LONGITUDINAL BACKBONE MEMBER THAT IS RESILIENTLY YIELDABLE IN TENSION, ANCHORED TO THE HUB, AND INCLUDING ALSO A NUMBER OF WEIGHT BARS WHICH ARE FASTENED TO THE BACK BONE MEMBER, DISPOSED TRANSVERELY OF THE BLADE AND SPACED AT INTERVALS ALONG THE BACKBONE MEMBER, EACH WEIGHT BAR BEING OF PREDETERMINED MASS, (C) FLEXIBLE BLADE SHEATHS, ONE FOR EACH BLADE, ENCLOSING THE CORRESPONDING BLADE FRAMES TO FORM THE WORKING SURFACES OF THE BLADES, AND ANCHORED IN THE RADIAL SENSE WITH RESPECT TO THE HUB, AND, (D) EACH LONGITUDINAL BACKBONE MEMBER AND SHEATH BEING ARRANGED TO TWIST TORSINALLY THROUGHOUT THE BLADES LENGTH UNDER MOMENTS APPLIED TO THE BACKBONE MEMBER BY THE WEIGHTS OF PREDETERMINED MASS, SUCH TWISTING BEING THEREBY VARIABLE IN ACCORDANCE WITH THE MAGNITUDE OF CENTRIFUGAL TWISTING MOMENTS INHERENT IN THE BLADE STRUCTURE AND ACTING ON THE MASS OF THE BLADE FRAMES AT DIFFERENT ROTATIONAL SPEEDS. 